U.S. patent number 7,679,247 [Application Number 11/820,255] was granted by the patent office on 2010-03-16 for lift magnet mechanism for flywheel power storage systems.
This patent grant is currently assigned to Beacon Power Corporation. Invention is credited to Jimpo Wang.
United States Patent |
7,679,247 |
Wang |
March 16, 2010 |
Lift magnet mechanism for flywheel power storage systems
Abstract
Electric power is stored in a flywheel assembly, from a dc power
buss, and supplied to the buss, through electronics associated with
a motor/generator, its rotor integral with a flywheel supported by
magnetic bearings. Upon operation, the flywheel assembly is
released by mechanical backup bearings which then normally remain
disengaged until shutdown as the flywheel assembly is levitated by
the axial magnetic field. Enhancements developed herein smooth the
flux density across discontinuities or segments present in
permanent magnets due to presently limited capability for
manufacture of large annular magnetic members. Herein, the
introduction of a medium such as a steel cylindrical member to
directly interface with the rotor as opposed to the segmented
permanent magnet, greatly eradicates induced eddy current and heat
on the rotor. In addition, exhibited is an annularly slotted rotor
which allows for greater surface area for flux absorption.
Inventors: |
Wang; Jimpo (Wilmington,
MA) |
Assignee: |
Beacon Power Corporation
(Tyngsboro, MA)
|
Family
ID: |
40135768 |
Appl.
No.: |
11/820,255 |
Filed: |
June 20, 2007 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
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US 20080315696 A1 |
Dec 25, 2008 |
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Current U.S.
Class: |
310/90.5; 310/74;
310/153; 310/15; 310/14 |
Current CPC
Class: |
F16C
32/0459 (20130101); H02K 7/09 (20130101); H02K
7/025 (20130101); Y02E 60/16 (20130101); F16C
2361/55 (20130101) |
Current International
Class: |
H02K
7/09 (20060101) |
Field of
Search: |
;310/12-39,74,90.5,153,216,269 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
PCT search report and written opinion dated Nov. 26, 2008 for
international application No. PCT/US 08/07709PCT. cited by
other.
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Primary Examiner: Leung; Quyen
Assistant Examiner: Kim; John K
Attorney, Agent or Firm: Pritzkau Patent Group LLC
Claims
I claim:
1. A flywheel levitation apparatus for a flywheel driven power
storage system, said apparatus comprising: a rotor having a rotor
face that faces upward in a vertical direction, and an axis of
rotation that is at least approximately aligned with said vertical
direction, and said rotor is supported for (i) rotation around said
axis and (ii) a limited amount of vertical movement along the axis
to provide for levitating the rotor; a stator assembly that is
configured to receive an electrical current and to generate a
magnetic flux therefrom; and at least one pole piece supported by
said stator and having a cylindrical projecting section, in the
form of a cylindrical member, having a cylindrical wall with a wall
thickness extending downward toward said rotor face and including a
lower surface that faces downward toward said rotor, and said
projecting section is configured for channeling said magnetic flux
toward said rotor to exert a magnetic lifting force upon said rotor
upward and in said vertical direction such that said lifting force
influences said vertical movement, wherein said rotor face defines
a cutaway section cooperatively arranged with said projecting
section in the form of an annular slot that is widthwise delimited
by a pair of opposing upwardly extending peripheral sidewalls,
having a width that is sufficient for receiving the wall thickness
of the pole piece, and the sidewalls are arranged such that said
projecting section is at least partially receivable in the cutaway
section, between said sidewalls, responsive to the vertical
movement of the rotor along said axis of rotation, and said annular
slot has a floor that faces upward in a confronting relationship
with said lower surface of said projecting section to define a gap,
having a gap size, between said rotor and said pole piece, and said
gap size changes in response to the vertical movement of the rotor
along said axis of rotation, and said magnetic lifting force
exhibits a gap sensitivity that is smaller as compared to a
conventional gap sensitivity that would be exhibited in an absence
of said cutaway section, and said rotor is operable in each one of
(i) a large gap configuration corresponding to a large gap size,
and (ii) a small gap configuration corresponding to a small gap
size, and at least a selected one of the pair of sidewalls
intersects a major surface of said rotor face to form a peripheral
edge such that the peripheral edge joins the selected sidewall with
the major surface, and in said large gap configuration a portion of
said magnetic flux is oriented from said projecting section towards
said peripheral edge to influence the magnetic levitation force
such that the magnetic levitation force is larger as compared to a
conventional large gap magnetic levitation force that would be
exhibited in a conventional flywheel levitation apparatus having
the same large gap size, and in the absence of said cutaway
section.
2. The flywheel levitation apparatus of claim 1 wherein each of
said pair of sidewalls is aligned in an approximately vertical
direction, and said sidewalls are arranged such that said pole
piece is at least partially receivable, responsive to said vertical
movement of the rotor, between said sidewalls.
3. A flywheel levitation apparatus for a flywheel driven power
storage system, said apparatus comprising: a rotor having a rotor
face that faces upward in a vertical direction, and an axis of
rotation that is at least approximately aligned with said vertical
direction, and said rotor is supported for (i) rotation around said
axis and (ii) a limited amount of vertical movement along the axis
to provide for levitating the rotor; a stator assembly that is
configured to receive an electrical current and to generate a
magnetic flux therefrom; and at least one pole piece supported by
said stator and having a cylindrical projecting section, in the
form of a cylindrical member, having a cylindrical wall with a wall
thickness extending downward toward said rotor face and including a
lower surface that faces downward toward said rotor, and said
projecting section is configured for channeling said magnetic flux
toward said rotor to exert a magnetic lifting force upon said rotor
upward and in said vertical direction such that said lifting force
influences said vertical movement, wherein said rotor face defines
a cutaway section cooperatively arranged with said projecting
section in the form of an annular slot that is widthwise delimited
by a pair of opposing upwardly extending peripheral sidewalls
having a width that is sufficient for receiving the wall thickness
of the pole piece, and the sidewalls are arranged such that said
projecting section is at least partially receivable in the cutaway
section, between said sidewalls, responsive to the vertical
movement of the rotor along said axis of rotation, and said annular
slot has a floor that faces upward in a confronting relationship
with said lower surface of said projecting section to define a gap,
having a gap size, between said rotor and said pole piece, and said
gap size changes in response to the vertical movement of the rotor
along said axis of rotation, and said magnetic lifting force
exhibits a gap sensitivity that is smaller as compared to a
conventional gap sensitivity that would be exhibited in an absence
of said cutaway section, and said rotor is operable in each one of
(i) a large gap configuration corresponding to a large gap size,
and (ii) a small gap configuration corresponding to a small gap
size, and said floor of said slot has a first width, and the rotor
face defines an upper opening leading into said slot and having a
second width, and at least one of said sidewalls is chamfered such
that the second width is larger than the first width, and said
sidewalls are arranged such that said pole piece is at least
partially receivable, responsive to said vertical movement of the
rotor, between said sidewalls.
4. The flywheel levitation apparatus of claim 3 wherein an inner
one of said pair of sidewalls is chamfered such that the inner
sidewall slants inward, towards the axis of rotation, and said
sidewalls are arranged such that said pole piece is at least
partially receivable, responsive to said vertical movement of the
rotor, between said sidewalls.
5. The flywheel levitation apparatus of claim 3 wherein an outer
one of said pair of sidewalls is chamfered such that the outer
sidewall slants outward, away from the axis of rotation, and said
sidewalls are arranged such that said pole piece is at least
partially receivable, responsive to said vertical movement of the
rotor, between said sidewalls.
Description
FIELD OF THE INVENTION
The present invention relates generally to flywheel driven power
storage systems and particularly to enhancements developed to
smooth the flux density across discontinuities or segments present
in permanent magnets due to present manufacturing capability.
REFERENCES
In general within the art, descriptions of flywheel driven power
storage systems and their various related elements can be found in
U.S. Pat. Nos. 5,614,777 set forth by Bitterly et al; 5,767,595,
5,708,312, 5,770,909, and 5,864,303 by Rosen et al; 3,860,300 and
4,147,396 by Lyman; 3,791,704 and 4,088,379 by Perper; 5,627,419 by
Miller; 4,910,449 by Hiyama et al: 5,760,510 by Nomura et al:
5,777,414 by Conrad; 5,319,844 by Huang et al; 4,444,444 by
Benedetti et al; 5,844,339 by Schroeder et al; 5,495,221,
5,783,885, 5,847,480, 5,861,690, and 5,883,499 by Post; 5,705,902
by Merritt et al; 5,044,944 and 5,311,092 by Fisher; 5,107,151 and
5,677,605 by Cambier et al; and 5,670,838 by Everton; plus
3,969,005, 3,989,324, 4,094,560, and 4,141,607 by Traut; and
4,799,809 by Kuroiwa.
More specific to the instant invention, U.S. Pat. No. 6,566,775
addresses use of electromagnets and permanent magnets to lift the
rotor off of the bearings in flywheel applications in order to
increase bearing life, reduce heat and eddy currents.
BACKGROUND OF INVENTION
This invention relates to electric power storage, through power
interface electronics and electromechanical energy conversion, in
the inertia of a spinning flywheel, and by reciprocal means, stored
kinetic energy conversion to electric power. The various component
elements of the invention include: A high-speed motor/generator,
with cooperative power electronics and magnetic bearings,
electronic feedback control servos to stabilize the magnetic
bearings, a vertical-axis flywheel, integral with the
motor/generator rotor and rotatable magnetic bearing elements, to
store kinetic energy, a vacuum enclosure to reduce air drag,
mechanical backup bearings that are not engaged during normal
service, and a stationary energy-absorbing installation site to
safely house the flywheel and its enclosure.
As also illustrated in the above-referenced United States patents,
such means as rechargeable electrochemical batteries offer some
usages, but encounter huge problems involving key issues such as
storage space, leakage and longevity. Therefore flywheel driven
systems may offer distinct advantages over such systems. However,
as flywheel power storage system designs have evolved from smaller,
physically limited structures with minimal storage capacity to the
high capacity systems employing industrial sized magnetic members
prevalent today, material restrictions and other such factors
inherent with have arisen. Said considerations must be overcome in
order to facilitate reaching the maximal energy storage and output
to render flywheel energy storage systems a viable alternative.
In modern applications, due to the need for extremely large
magnetic arrays and magnetic members, current manufacturing
capabilities restrict magnetic arrays to structures containing
joined magnetic segments. Due to the inherent discontinuities in
flux density across these segments occurring upon interface of the
rotor and stator, if faced directly with rotor, the permanent
magnet array will induce eddy current and excess heat upon the
rotor. Thus, in order to address this shortcoming, what is needed
is a mechanism and/or system which works to eradicate these
problems by vitiating or smoothing out the discontinuities from the
segments.
Additionally, in modern larger applications, magnetic force
generated either by permanent magnet or electromagnet or the
combination of both is used to lift the rotor in a flywheel system.
Magnetic force generated by a pair of stationary stator and rotor
is normally highly sensitive to the air gap separating the stator
and rotor. High sensitivity implies low magnetic force as the gap
is large and excessively high force as the gap is small. Lower
force at the large gap requires designs with either stronger
magnets or higher current to lift the rotor, and excessively high
force at small gap would potentially damage the parts under the
fault conditions.
Previous failure of high capacity flywheel systems often is found
to be triggered by overloading and overheating of the touchdown
ball bearing. When utilizing a pure electromagnet lift magnet,
failure offer occurs as the electrical power is tripped during
normal operation due to the high lifting force requirement. As the
lifting force dissipates, the heavy rotor will then sit on the ball
bearings, and thus, due to the heavy load, will heat up the ball
bearings in a short expense of time. Thus, as the ball bearing
fails, the high speed rotor loses the mechanical support, and
rotates basically out of round, contacting the casing. Thus, wear,
catastrophic at times and even explosions within the casing may
occur.
Further, in systems utilizing magnetic force generated either by a
permanent magnet or electromagnet or the combination of both to
lift the rotor, the magnetic force generated by a pair of
stationary stators and rotor is normally highly sensitive to the
air gap separating the stator and rotor. High sensitivity implies
that low magnetic force occurs when the gap is large in magnitude
and excessively high force occurs when the gap is small in
magnitude. The larger gap condition at which lower force occurs
requires designs with either stronger magnets or higher current to
lift the rotor; whereas, on the other hand, the excessively high
force at small gap could potentially damage parts or the overall
system under fault conditions.
Therefore, when investigating the typical lift magnet design, what
is needed is a design that can provide magnetic force with low gap
sensitivity, for the conditions at which the magnetic force is
moderately higher at the large gap configuration and significantly
lower at the small gap configuration. Additionally, what is needed
is a system, mechanism or method of operation, which minimizes the
load on the ball bearings in the case where the rotor drops on the
bearing for any potential failure mode. Also needed is a system to
prevent the high speed rotor form sticking to the stator under any
potential failure mode while also minimizing the electrical power
used in the lift magnet system to minimize the heat generation
which lends to superior control of the rotor.
SUMMARY OF THE INVENTION
The instant invention, as illustrated herein, is clearly not
anticipated, rendered obvious, or even present in any of the prior
art mechanisms, either alone or in any combination thereof. A
flywheel driven power storage system, adapted to compensate for the
aforementioned drawbacks and limitations would afford significant
improvement to numerous useful applications. Thus the several
embodiments of the instant invention are illustrated herein.
The salient objectives of the instant invention center around
improvement of high capacity, flywheel energy storage systems and
particularly around improvement upon inherent bearing wear, control
of magnetic flux and minimization of required lift power
fluctuation. Thus, creation of a system, subsystem, mechanism or
method of operation which minimizes the load on the ball bearings,
in the case where the high speed rotor should release and begin to
plummet down on the ball bearings during potential failure mode, is
crucial.
It is an additional objective of the instant invention to provide a
flywheel power storage system possessing a motor/generator with
minimal eddy current losses which displays use of mechanical
bearings only as temporary backup as a rotor integral primary
magnetically driven primary bearing system relieves wear on the
mechanical bearings.
Further, as in any flywheel driven system, general objectives of
this invention are to provide improved long-life flywheel batteries
without sizable power losses, excessive internal heating, vacuum
loss, extensive maintenance, explosion hazard and high cost.
It is an added objective of the instant invention to prevent the
high speed rotor from becoming affixed to the stator due to extreme
force and heat considerations experienced under any potential
failure mode.
It is a further objective of the instant invention to enable the
flywheel system to operate under cooler conditions and thus prevent
inherent overheating and rotor and stator attachment, or
sticking.
Another objective of the instant invention is to minimize the
electrical power used in the lift magnet system, which inherently
minimizes the heat generation, but additionally maintain proper
control of the rotor.
Another objective of the instant invention is to provide an
apparatus comprising a cylindrically shaped steel pole mechanism
disposed to cover the segmented magnet array and thus during
interface with any configuration of stator in order to minimize the
eddy current and ambient heat. Thus use of said apparatus
inherently minimizes stator winding heating, resulting thermal
stresses, and possible outgassing of resin molding when such
materials are utilized.
It is another objective of the instant invention to introduce an
apparatus that provides magnetic force with low gap sensitivity and
wherein the magnetic force is moderately higher at the large gap
and significantly lower at the small gap.
Another objective is to eliminate need for lubricants in mechanical
backup bearings, to remove a cause of vacuum loss, frequent
maintenance, and mechanical bearing failures.
Thus, one specific objective of the instant invention is to provide
a system that eradicates the power spikes generated by prior
systems due to physical spacing consideration inherent in
applications possessing large circular pieced together magnet
members.
Accordingly, an improved flywheel battery system and accompanying
enhancements its component elements are herein described, which
achieve these objectives, plus other advantages and enhancements.
These improvements to the art will be apparent from the following
description of the invention when considered in conjunction with
the accompanying drawings wherein there has thus been outlined,
rather broadly, the more important features of the vehicle
monitoring system in order that the detailed description thereof
that follows may be better understood, and in order that the
present contribution to the art may be better appreciated.
There are additional features of the invention that will be
described hereinafter and which will form the subject matter of the
claims appended hereto. In this respect, before explaining at least
one embodiment of the invention in detail, it is to be understood
that the invention is not limited in its application to the details
of construction and to the arrangements of the components set forth
in the following description or illustrated in the drawings. The
invention is capable of other embodiments and of being practiced
and carried out in various ways. Also, it is to be understood that
the phraseology and terminology employed herein are for the purpose
of the description and should not be regarded as limiting.
These together with other objects of the invention, along with the
various features of novelty, which characterize the invention, are
pointed out with particularity in the claims annexed to and forming
a part of this disclosure. For a better understanding of the
invention, its operating advantages and the specific objects
attained by its uses, reference should be made to the accompanying
drawings and descriptive matter in which there are illustrated
preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIG. 1 illustrates a simplified cutaway assembly block diagram of
the magnetic lift portion of the instant flywheel battery,
illustrating the stator housing, the permanent magnet array which
is comprised of segmented magnet array and the steel cylindrical
member or pole, the coil, and the rotor, centered around the axis
of rotation;
FIG. 2 is a top view of the permanent magnet array illustrating the
segmented nature of the segmented magnet array;
FIG. 3 is block diagram illustrating the steel cylindrical member
or pole;
FIG. 4 is a side view of the rotor in the slotted embodiment;
FIG. 5 is a side view of the rotor, illustrating the slotted
construction in a chamfered embodiment;
FIG. 6 is a finite element analysis readout illustrating the
magnetic flux created when utilizing a slotted rotor at a small gap
between rotor and stator;
FIG. 7 is a finite element analysis readout illustrating the
magnetic flux created when utilizing a slotted rotor at a large gap
between rotor and stator;
FIG. 8, a graphical representation, illustrates that the due to the
use of the slotted rotor, the differential between lifting force
needed from large rotor/stator gap to small rotor/stator gap,
becomes dramatically lessened than the differential between lifting
force with the prior rotors.
FIG. 9 illustrates a side cutaway view of the novel assembly within
an actual flywheel power storage system.
FIG. 10 is a side cross-sectional three dimensional view of the
overall apparatus illustrating the flywheel power storage system
magnetic ring apparatus, illustrating the stator housing and
assembly, the permanent magnet array which is comprised of
segmented magnet array and the steel cylindrical member or pole,
the coil, the gap between rotor and stator, or rotor/stator gap,
and the rotor including the slot.
FIG. 11 is a side cross-sectional view exhibiting the rotor
attached to its vertical-axis spindle which interfaces with the
flywheel rim, is axially levitated by attraction forces between
high permeability steel at the upper end of rotor, and the
interaction of the segmented magnet array.
FIG. 12 is isometric cutaway view of the invention illustrating all
of the elements.
DETAILED DESCRIPTION OF THE EMBODIMENTS
In flywheel driven power storage systems, the magnetic force
generated either by permanent magnet or electromagnet or the
combination of both is used to lift the rotor in a flywheel system.
The magnetic force generated by a pair of stationary stator and
rotor is normally highly sensitive to the air gap separating the
stator and rotor. High sensitivity implies low magnetic force, as
the gap is large and excessively high force as the gap is
small.
In order illustrate the numerous embodiments of the instant
invention, referring first to FIG. 1 illustrates a simplified
cutaway assembly block diagram of the flywheel power storage system
magnetic ring apparatus 10 or magnetic lift portion of the instant
flywheel battery, illustrating the stator housing and assembly 20,
the permanent magnet array 30 which is comprised of segmented
magnet array 31 and the steel cylindrical member 40 or pole 40, the
coil 50, the gap between rotor and stator, or rotor/stator gap 60,
and the rotor 70 including the slot 80.
Next, referring to FIG. 2 is a top view of the permanent magnet
array 30, illustrating the individual segments 90 of the magnet
array. FIG. 3 is a block diagram illustrating the steel cylindrical
member 40 or pole 40, designed to compensate for the segmented
magnet array 31 and the discontinuity of the individual segments 90
which is problematic because it induces the magnetic flux variation
which in turn generates the heat on the rotating member.
FIG. 4 is a side view of the rotor 70, illustrating the novel
slotted construction 80, which allows for greater surface area for
further magnetic flux leakage to the walls and thus for more ready
control of fluctuation in lifting force. FIG. 5 is a side view of
the rotor 70, illustrating the slotted construction 80 in a
chamfered version 81, which additionally allows for more surface
area for further magnetic flux leakage to the walls for more ready
control of fluctuation in lifting force.
FIG. 6 is a readout of a finite element analysis illustrating the
magnetic flux 101 created when utilizing a slotted rotor 80 at a
small gap between rotor 70 and stator housing and assembly 20.
Similarly, FIG. 7 is a readout of a finite element analysis
illustrating the magnetic flux 102 created when utilizing a slotted
rotor at a large gap between rotor and stator.
As illustrated in FIG. 8, graphical representation, due to the use
of the slotted rotor 80, the differential between lifting force
needed from large rotor/stator gap to small rotor/stator gap 121
with the slotted rotor, becomes dramatically lessened than the
differential between lifting force with the prior rotors 122.
FIG. 9 illustrates a side cutaway view of the instant magnetic ring
or magnetic lift system 10 within an actual flywheel power storage
system. FIG. 10 is a side cross-sectional three dimensional view of
the overall apparatus illustrating the flywheel power storage
system magnetic ring apparatus 10, illustrating the stator housing
and assembly 20, the permanent magnet array 30 which is comprised
of segmented magnet array 31 and the steel cylindrical member 40 or
pole 40, the coil 50, the gap between rotor and stator, or
rotor/stator gap 60, and the rotor 70 including the slot 80.
With reference to FIG. 11, the rotor 70, attached to its
vertical-axis spindle 71 and to flywheel rim 120, is axially
levitated by attraction forces between high permeability steel or
other appropriate material located at the upper end of rotor 70 and
the non-rotating segmented magnet array 31 and the non-rotating,
high-permeability, annular steel cylindrical member 40 or pole 40,
located at the upper and lower side of the non-rotating, annular,
axially-magnetized, permanent magnet array 30. Concentric coil 50,
which performs as an electromagnet, is provided bi-directional
drive current and the overall evolutional provides inherently
stable centering forces, due to the same magnetic field that
provides axial levitation for the flywheel rim 120.
This ability to magnetically levitate the flywheel rim during
operation allows for great reduction in normal wear on bearings,
magnetic members and steel members and also minimizes ill effects
such as eddy current losses, plastic deformity or the like,
specifically because no iron, high-permeability steel or magnet
members are subjected to continuous magnetic flux cycling, nor to
substantial magnetic flux variation, due to rotor spin. This
condition holds especially true as the steel cylindrical member in
the instant invention replaces the permanent magnet in interfacing
with the rotor, thus smoothing the magnetic flux.
As illustrated herein, in order to avoid overloading and
overheating of the ball bearings as the rotor drops on the bearing
system, the instant invention introduces a hybrid type of lift
magnet system which includes the permanent magnet array to provide
the majority of the lifting force to ensure the ball bearing system
will not be overloaded, even upon failure of the electromagnet
system. Our permanent magnet array is made of segment magnets
covered with magnetic steel pole which smoothes the flux density to
avoid eddy current loss and heat generation on the rotor. The
electromagnet in the instant lift magnet system only provides a
small portion of the lifting force to control the rotor/stator
gap.
With the instant permanent magnet array, much lower current and
power is required for the electromagnet. The instant flywheel
system will operate and remain cooler with less heat generation,
while the slotted rotor provides a relatively constant lifting
force. As discussed above in the background section, when
investigating the typical lift magnet design, what is needed is a
design that can provide magnetic force with low gap sensitivity,
for the conditions at which the magnetic force is moderately higher
at the large gap configuration and significantly lower at the small
gap configuration. Compared with the usual rotors lacking the
slotted arrangement, the instant slotted rotor design provides the
aforementioned needed characteristics, including greater lifting
force at the large gap configuration and significantly lower
lifting force at the small gap configuration.
While several embodiments of the present invention have been
illustrated by way of example, it is apparent that further
embodiments could be developed within the spirit and scope of the
present invention. However, it is to be expressly understood that
such modifications and adaptations are within the spirit and scope
of the present invention, as set forth in the following appended
claims.
* * * * *